Chapter 54
Ecosystems
PowerPoint Lectures for
Biology, Seventh Edition
Neil Campbell and Jane Reece
Lectures by Chris Romero
Copyright © 2005 Pearson Education, Inc. publishing as Benjamin Cummings
• Overview: Ecosystems, Energy, and Matter
• An ecosystem consists of all the organisms
living in a community
– As well as all the abiotic factors with which
they interact
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• Ecosystems can range from a microcosm, such
as an aquarium
– To a large area such as a lake or forest
Figure 54.1
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• Regardless of an ecosystem’s size
– Its dynamics involve two main processes:
energy flow and chemical cycling
• Energy flows through ecosystems
– While matter cycles within them
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• Concept 54.1: Ecosystem ecology emphasizes
energy flow and chemical cycling
• Ecosystem ecologists view ecosystems
– As transformers of energy and processors of
matter
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Ecosystems and Physical Laws
• The laws of physics and chemistry apply to
ecosystems
– Particularly in regard to the flow of energy
• Energy is conserved
– But degraded to heat during ecosystem
processes
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Trophic Relationships
• Energy and nutrients pass from primary
producers (autotrophs)
– To primary consumers (herbivores) and then to
secondary consumers (carnivores)
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• Energy flows through an ecosystem
– Entering as light and exiting as heat
Tertiary
consumers
Microorganisms
and other
detritivores
Detritus
Secondary
consumers
Primary consumers
Primary producers
Heat
Key
Chemical cycling
Energy flow
Figure 54.2
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Sun
• Nutrients cycle within an ecosystem
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Decomposition
• Decomposition
– Connects all trophic levels
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• Detritivores, mainly bacteria and fungi, recycle
essential chemical elements
– By decomposing organic material and returning
elements to inorganic reservoirs
Figure 54.3
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• Concept 54.2: Physical and chemical factors
limit primary production in ecosystems
• Primary production in an ecosystem
– Is the amount of light energy converted to
chemical energy by autotrophs during a given
time period
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Ecosystem Energy Budgets
• The extent of photosynthetic production
– Sets the spending limit for the energy budget
of the entire ecosystem
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The Global Energy Budget
• The amount of solar radiation reaching the
surface of the Earth
– Limits the photosynthetic output of ecosystems
• Only a small fraction of solar energy
– Actually strikes photosynthetic organisms
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Gross and Net Primary Production
• Total primary production in an ecosystem
– Is known as that ecosystem’s gross primary
production (GPP)
• Not all of this production
– Is stored as organic material in the growing
plants
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• Net primary production (NPP)
– Is equal to GPP minus the energy used by the
primary producers for respiration
• Only NPP
– Is available to consumers
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• Different ecosystems vary considerably in their net
primary production
– And in their contribution to the total NPP on Earth
Open ocean
Continental shelf
Estuary
5.2
0.3
0.1
0.1
Algal beds and reefs
Upwelling zones
Extreme desert, rock, sand, ice
4.7
Desert and semidesert scrub
Tropical rain forest
3.5
3.3
2.9
2.7
Savanna
Cultivated land
Boreal forest (taiga)
1.6
Tropical seasonal forest
Temperate deciduous forest
1.5
1.3
1.0
0.4
Temperate evergreen forest
Swamp and marsh
Lake and stream
Marine
10
3.0
90
0.04
0.9
2,200
22
900
7.9
9.1
600
9.6
800
600
700
5.4
3.5
0.6
140
1,600
7.1
1,200
1,300
4.9
3.8
2.3
0.3
2,000
250
20
30
40
50
60
(a) Percentage of Earth’s
surface area
0
500 1,000 1,500 2,000 2,500
(b) Average net primary
production (g/m2/yr)
Terrestrial
Freshwater (on continents)
0.9
0.1
500
0.4
0
1.2
2,500
1.7
Tundra
24.4
5.6
1,500
2.4
1.8
Temperate grassland
Woodland and shrubland
Key
125
360
65.0
Figure 54.4a–c
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0
5
10
15
20
(c) Percentage of Earth’s net
primary production
25
• Overall, terrestrial ecosystems
– Contribute about two-thirds of global NPP and
marine ecosystems about one-third
North Pole
60N
30N
Equator
30S
60S
South Pole
180
120W
60W
Figure 54.5
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0
60E
120E
180
Primary Production in Marine and Freshwater
Ecosystems
• In marine and freshwater ecosystems
– Both light and nutrients are important in
controlling primary production
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Light Limitation
• The depth of light penetration
– Affects primary production throughout the
photic zone of an ocean or lake
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Nutrient Limitation
• More than light, nutrients limit primary
production
– Both in different geographic regions of the
ocean and in lakes
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• A limiting nutrient is the element that must be
added
– In order for production to increase in a
particular area
• Nitrogen and phosphorous
– Are typically the nutrients that most often limit
marine production
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• Nutrient enrichment experiments
– Confirmed that nitrogen was limiting phytoplankton
growth in an area of the ocean
EXPERIMENT
Pollution from duck farms concentrated near
Moriches Bay adds both nitrogen and phosphorus to the coastal water
off Long Island. Researchers cultured the phytoplankton Nannochloris
atomus with water collected from several bays.
30
21
19
15
5
4
Coast of Long Island, New York.
The numbers on the map indicate
the data collection stations.
Figure 54.6
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2
11
Shinnecock
Bay
Moriches Bay
Atlantic Ocean
Inorganic
phosphorus
5
4
3
2
1
8
7
6
5
4
3
2
1
0
0
2
4
5
11 30 15 19 21
Station number
Great
Moriches
South Bay
Bay
30
Phytoplankton
(millions of cells per mL)
Phytoplankton
8
7
6
Inorganic phosphorus
(g atoms/L)
Phytoplankton
(millions of cells/mL)
RESULTS Phytoplankton abundance parallels the abundance of phosphorus in the water (a). Nitrogen,
however, is immediately taken up by algae, and no free nitrogen is measured in the coastal waters. The
addition of ammonium (NH4) caused heavy phytoplankton growth in bay water, but the addition of
phosphate (PO43) did not induce algal growth (b).
24
Ammonium enriched
Phosphate enriched
Unenriched control
18
12
6
0
Shinnecock
Bay
(a) Phytoplankton biomass and phosphorus concentration
Starting 2
algal
density
4
5 11 30
Station number
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19
(b) Phytoplankton response to nutrient enrichment
Since adding phosphorus, which was already in rich supply, had no effect on
CONCLUSION
Nannochloris growth, whereas adding nitrogen increased algal density dramatically, researchers
concluded that nitrogen was the nutrient limiting phytoplankton growth in this ecosystem.
Figure 54.6
15
21
• Experiments in another ocean region
– Showed that iron limited primary production
Table 54.1
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• The addition of large amounts of nutrients to
lakes
– Has a wide range of ecological impacts
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• In some areas, sewage runoff
– Has caused eutrophication of lakes, which can
lead to the eventual loss of most fish species from
the lakes
Figure 54.7
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Primary Production in Terrestrial and Wetland
Ecosystems
• In terrestrial and wetland ecosystems climatic
factors
– Such as temperature and moisture, affect
primary production on a large geographic scale
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• The contrast between wet and dry climates
– Can be represented by a measure called
actual evapotranspiration
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• Actual evapotranspiration
– Is the amount of water annually transpired by plants
and evaporated from a landscape
– Is related to net primary production
Net primary production (g/m2/yr)
3,000
Tropical forest
2,000
Temperate forest
1,000
Mountain coniferous forest
Desert
shrubland
Temperate grassland
Arctic tundra
0
0
500
1,000
1,500
Actual evapotranspiration (mm H2O/yr)
Figure 54.8
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• On a more local scale
– A soil nutrient is often the limiting factor in primary
production
EXPERIMENT
Live, above-ground biomass
(g dry wt/m2)
Over the summer of 1980, researchers added
phosphorus to some experimental plots in the salt marsh, nitrogen
to other plots, and both phosphorus and nitrogen to others. Some
plots were left unfertilized as controls.
Adding nitrogen (N)
boosts net primary
RESULTS
production.
300
NP
250
200
150
N only
100
Control
50
P only
0
July
June
August 1980
Experimental plots receiving just
phosphorus (P) do not outproduce
the unfertilized control plots.
CONCLUSION
Figure 54.9
These nutrient enrichment experiments
confirmed that nitrogen was the nutrient limiting plant growth in
this salt marsh.
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• Concept 54.3: Energy transfer between trophic
levels is usually less than 20% efficient
• The secondary production of an ecosystem
– Is the amount of chemical energy in
consumers’ food that is converted to their own
new biomass during a given period of time
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Production Efficiency
• When a caterpillar feeds on a plant leaf
– Only about one-sixth of the energy in the leaf
is used for secondary production
Plant material
eaten by caterpillar
200 J
67 J
Feces
100 J
33 J
Figure 54.10
Growth (new biomass)
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Cellular
respiration
• The production efficiency of an organism
– Is the fraction of energy stored in food that is
not used for respiration
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Trophic Efficiency and Ecological Pyramids
• Trophic efficiency
– Is the percentage of production transferred
from one trophic level to the next
– Usually ranges from 5% to 20%
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Pyramids of Production
• This loss of energy with each transfer in a food chain
– Can be represented by a pyramid of net production
Tertiary
consumers
Secondary
consumers
Primary
consumers
Primary
producers
Figure 54.11
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10 J
100 J
1,000 J
10,000 J
1,000,000 J of sunlight
Pyramids of Biomass
• One important ecological consequence of low
trophic efficiencies
– Can be represented in a biomass pyramid
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• Most biomass pyramids
– Show a sharp decrease at successively higher
trophic levels
Trophic level
Dry weight
(g/m2)
Tertiary consumers
1.5
Secondary consumers
11
Primary consumers
Primary producers
(a) Most biomass pyramids show a sharp decrease in biomass at
successively higher trophic levels, as illustrated by data from
a bog at Silver Springs, Florida.
Figure 54.12a
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37
809
• Certain aquatic ecosystems
– Have inverted biomass pyramids
Trophic level
Dry weight
(g/m2)
Primary consumers (zooplankton)
21
Primary producers (phytoplankton)
4
(b) In some aquatic ecosystems, such as the English Channel,
a small standing crop of primary producers (phytoplankton)
supports a larger standing crop of primary consumers (zooplankton).
Figire 54.12b
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Pyramids of Numbers
• A pyramid of numbers
– Represents the number of individual
organisms in each trophic level
Trophic level
Tertiary consumers
Number of
individual organisms
3
Secondary consumers
354,904
Primary consumers
708,624
Primary producers
Figure 54.13
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5,842,424
• The dynamics of energy flow through
ecosystems
– Have important implications for the human
population
• Eating meat
– Is a relatively inefficient way of tapping
photosynthetic production
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• Worldwide agriculture could successfully feed
many more people
– If humans all fed more efficiently, eating only
plant material
Trophic level
Secondary
consumers
Primary
consumers
Primary
producers
Figure 54.14
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The Green World Hypothesis
• According to the green world hypothesis
– Terrestrial herbivores consume relatively little
plant biomass because they are held in check
by a variety of factors
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• Most terrestrial ecosystems
– Have large standing crops despite the large
numbers of herbivores
Figure 54.15
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• The green world hypothesis proposes several
factors that keep herbivores in check
– Plants have defenses against herbivores
– Nutrients, not energy supply, usually limit
herbivores
– Abiotic factors limit herbivores
– Intraspecific competition can limit herbivore
numbers
– Interspecific interactions check herbivore
densities
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• Concept 54.4: Biological and geochemical
processes move nutrients between organic and
inorganic parts of the ecosystem
• Life on Earth
– Depends on the recycling of essential chemical
elements
• Nutrient circuits that cycle matter through an
ecosystem
– Involve both biotic and abiotic components and
are often called biogeochemical cycles
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A General Model of Chemical Cycling
• Gaseous forms of carbon, oxygen, sulfur, and
nitrogen
– Occur in the atmosphere and cycle globally
• Less mobile elements, including phosphorous,
potassium, and calcium
– Cycle on a more local level
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• A general model of nutrient cycling
– Includes the main reservoirs of elements and
the processes that transfer elements between
reservoirs
Reservoir a
Organic
materials
available
as nutrients
Living
organisms,
detritus
Assimilation,
photosynthesis
Figure 54.16
Reservoir b
Organic
materials
unavailable
as nutrients
Fossilization
Coal, oil,
peat
Respiration,
decomposition,
excretion
Burning
of fossil fuels
Reservoir c
Reservoir d
Inorganic
materials
available
as nutrients
Inorganic
materials
unavailable
as nutrients
Atmosphere,
soil, water
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Weathering,
erosion
Formation of
sedimentary rock
Minerals
in rocks
• All elements
– Cycle between organic and inorganic
reservoirs
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Biogeochemical Cycles
• The water cycle and the carbon cycle
THE CARBON CYCLE
THE WATER CYCLE
CO2 in atmosphere
Transport
over land
Photosynthesis
Solar energy
Cellular
respiration
Net movement of
water vapor by wind
Precipitation
over ocean
Evaporation
from ocean
Precipitation
over land
Burning of
fossil fuels
and wood
Evapotranspiration
from land
Percolation
through
soil
Runoff and
groundwater
Figure 54.17
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Carbon compounds
in water
Higher-level
Primary consumers
consumers
Detritus
Decomposition
• Water moves in a global cycle
– Driven by solar energy
• The carbon cycle
– Reflects the reciprocal processes of
photosynthesis and cellular respiration
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• The nitrogen cycle and the phosphorous cycle
THE PHOSPHORUS CYCLE
THE NITROGEN CYCLE
N2 in atmosphere
Rain
Geologic
uplift
Runoff
Assimilation
NO3
Nitrogen-fixing
bacteria in root
nodules of legumes
Plants
Weathering
of rocks
Denitrifying
bacteria
Consumption
Sedimentation
Decomposers
Ammonification
NH3
Nitrogen-fixing
soil bacteria
Nitrifying
bacteria
Nitrification
Soil
Plant uptake
of PO43
Leaching
NO2 
NH4+
Nitrifying
bacteria
Figure 54.17
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Decomposition
• Most of the nitrogen cycling in natural
ecosystems
– Involves local cycles between organisms and
soil or water
• The phosphorus cycle
– Is relatively localized
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Decomposition and Nutrient Cycling Rates
• Decomposers (detritivores) play a key role
– In the general pattern of chemical cycling
Consumers
Producers
Decomposers
Nutrients
available
to producers
Abiotic
reservoir
Figure 54.18
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Geologic
processes
• The rates at which nutrients cycle in different
ecosystems
– Are extremely variable, mostly as a result of
differences in rates of decomposition
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Vegetation and Nutrient Cycling: The Hubbard
Brook Experimental Forest
• Nutrient cycling
– Is strongly regulated by vegetation
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• Long-term ecological research projects
– Monitor ecosystem dynamics over relatively
long periods of time
• The Hubbard Brook Experimental Forest
– Has been used to study nutrient cycling in a
forest ecosystem since 1963
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• The research team constructed a dam on the
site
– To monitor water and mineral loss
Figure 54.19a
(a) Concrete dams and weirs built across streams at
the bottom of watersheds enabled researchers to
monitor the outflow of water and nutrients from the
ecosystem.
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• In one experiment, the trees in one valley were
cut down
– And the valley was sprayed with herbicides
Figure 54.19b
(b) One watershed was clear cut to study the effects of the loss
of vegetation on drainage and nutrient cycling.
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• Net losses of water and minerals were studied
– And found to be greater than in an undisturbed area
• These results showed how human activity
Nitrate concentration in runoff
(mg/L)
– Can affect ecosystems
80.0
60.0
40.0
20.0
4.0
3.0
2.0
1.0
0
Deforested
Completion of
tree cutting
1965
Figure 54.19c
Control
1966
1967
1968
(c) The concentration of nitrate in runoff from the deforested watershed was 60 times
greater than in a control (unlogged) watershed.
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• Concept 54.5: The human population is
disrupting chemical cycles throughout the
biosphere
• As the human population has grown in size
– Our activities have disrupted the trophic
structure, energy flow, and chemical cycling of
ecosystems in most parts of the world
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Nutrient Enrichment
• In addition to transporting nutrients from one
location to another
– Humans have added entirely new materials,
some of them toxins, to ecosystems
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Agriculture and Nitrogen Cycling
• Agriculture constantly removes nutrients from
ecosystems
– That would ordinarily be cycled back into the soil
Figure 54.20
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• Nitrogen is the main nutrient lost through
agriculture
– Thus, agriculture has a great impact on the
nitrogen cycle
• Industrially produced fertilizer is typically used
to replace lost nitrogen
– But the effects on an ecosystem can be
harmful
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Contamination of Aquatic Ecosystems
• The critical load for a nutrient
– Is the amount of that nutrient that can be
absorbed by plants in an ecosystem without
damaging it
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• When excess nutrients are added to an
ecosystem, the critical load is exceeded
– And the remaining nutrients can contaminate
groundwater and freshwater and marine
ecosystems
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• Sewage runoff contaminates freshwater
ecosystems
– Causing cultural eutrophication, excessive
algal growth, which can cause significant harm
to these ecosystems
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Acid Precipitation
• Combustion of fossil fuels
– Is the main cause of acid precipitation
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• North American and European ecosystems
downwind from industrial regions
– Have been damaged by rain and snow containing
nitric and sulfuric acid
4.6
4.3
4.6
4.3
4.6
4.1
4.3
4.6
Europe
Figure 54.21
North America
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• By the year 2000
– The entire contiguous United States was affected by
acid precipitation
Figure 54.22
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Field pH
5.3
5.2–5.3
5.1–5.2
5.0–5.1
4.9–5.0
4.8–4.9
4.7–4.8
4.6–4.7
4.5–4.6
4.4–4.5
4.3–4.4
4.3
• Environmental regulations and new industrial
technologies
– Have allowed many developed countries to
reduce sulfur dioxide emissions in the past 30
years
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Toxins in the Environment
• Humans release an immense variety of toxic
chemicals
– Including thousands of synthetics previously
unknown to nature
• One of the reasons such toxins are so harmful
– Is that they become more concentrated in
successive trophic levels of a food web
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• In biological magnification
– Toxins concentrate at higher trophic levels
because at these levels biomass tends to be lower
Concentration of PCBs
Herring
gull eggs
124 ppm
Figure 54.23
Lake trout
4.83 ppm
Smelt
1.04 ppm
Zooplankton
0.123 ppm
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Phytoplankton
0.025 ppm
• In some cases, harmful substances
– Persist for long periods of time in an
ecosystem and continue to cause harm
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Atmospheric Carbon Dioxide
• One pressing problem caused by human
activities
– Is the rising level of atmospheric carbon
dioxide
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Rising Atmospheric CO2
• Due to the increased burning of fossil fuels and
other human activities
390
1.05
380
0.90
0.75
370
Temperature
0.60
360
0.45
350
0.30
340
CO2
330
0.15
0
Temperature variation (C)
CO2 concentration (ppm)
– The concentration of atmospheric CO2 has been
steadily increasing
320
0.15
310
 0.30
300
1960 1965 1970 1975
Figure 54.24
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 0.45
1980 1985 1990 1995 2000 2005
Year
How Elevated CO2 Affects Forest Ecology: The
FACTS-I Experiment
• The FACTS-I experiment is testing how elevated CO2
– Influences tree growth, carbon concentration in soils,
and other factors over a ten-year period
Figure 54.25
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The Greenhouse Effect and Global Warming
• The greenhouse effect is caused by
atmospheric CO2
– But is necessary to keep the surface of the
Earth at a habitable temperature
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• Increased levels of atmospheric CO2 are
magnifying the greenhouse effect
– Which could cause global warming and
significant climatic change
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Depletion of Atmospheric Ozone
• Life on Earth is protected from the damaging
effects of UV radiation
– By a protective layer or ozone molecules
present in the atmosphere
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• Satellite studies of the atmosphere
– Suggest that the ozone layer has been gradually
thinning since 1975
Ozone layer thickness (Dobson units)
350
300
250
200
150
100
50
0
1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Figure 54.26
Year (Average for the month of October)
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• The destruction of atmospheric ozone
– Probably results from chlorine-releasing
pollutants produced by human activity
1 Chlorine from CFCs interacts with ozone (O3),
forming chlorine monoxide (ClO) and
oxygen (O2).
Chlorine atoms
O2
Chlorine
O3
ClO
O2
Figure 54.27
3 Sunlight causes
Cl2O2 to break
down into O2
and free
chlorine atoms.
The chlorine
atoms can begin
the cycle again.
ClO
Cl2O2
Sunlight
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2 Two ClO molecules
react, forming
chlorine peroxide (Cl2O2).
• Scientists first described an “ozone hole”
– Over Antarctica in 1985; it has increased in
size as ozone depletion has increased
(a) October 1979
Figure 54.28a, b
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(b) October 2000